Coated paper and substance for coating the same



Patented Feb. T35, 1923.

UNHTEID stares smear castes.

HENRY N. CASE, OF OAK PARK, ILLINOIS, ASSIGNOR TO SEARS, ROEBUCK AND CO., OF

CHICAGO, ILLINOIS, A CORPORATION OF NEW YORK.

COATED PAPER AND SUBSTANCE FOR COATING THE SAME.

No Drawing.

T all whom it may concern:

Be it known that I, HENRY N. CASE, a

citizen of the United States, residing at Oak Park, in the county of Cook and State of Illinois, have invented an Improved Coated Paper and Substance for Coating the Same, of which the following is a specification.

This invention relates to a paper base coated on both sides with material capable of being etched to produce reliefs suitable for use as matrices in subjecting printing plates to the McKee process. One of the greatest difliculties in making such coated paper is to avoid conditions which will prevent the finished matrix from being the exact size of the printing plate with which the matrix is to be used. Another serious difliculty is to make the coatings of uniform thickness.

The object of this invention is to produce a highgrade coated paper, and to provide a bath for coating the paper which eliminates the difficulties heretofore encountered in manufacturing such paper.

The process for applying the coating material to the paper is claimed in my co pending applications, Serial Nos. 2807 50 and 370,542 filed March 5, 1919 and April 1,

1920, respectively, and no claim 7 to such process is therefore made herein.

While the paper base may be of any suitable character, I have obtained good results with a paper stock having a base weight of 24 lbs. per ream of 17x22 sheets; a thick ness of four one-thousandths of an inch,

' with very slight calendering; all-rag fiber, preferably all cotton; capable of standing a degree Baum bleach for five minutes with- 40 out becoming too tender to stand rough handling; which will not shrink or expand one one-hundredth of an inch per foot in either direction when soaked in water and Edried in the air; and which is beater-sized and tub-sized, the sizing being free from ,grease. The paper may be of any suitable width, as, for example, 18 inches, and is 7 preferably supplied in the form of rolls of convenient diameter. 5o \Vithout intending to limit myself to any Application filed March 5, 1919. Serial No. 280,751.

particular ingredients or to any particular proportlons thereof, it may be stated that good results have been obtained with a solution or mixture formed of the following ingred1ents:

Clay, 39 lbs; water for the clay, 28 lbs; gelatine, 74: oz.; water for the gelatine, 15 pints.

The clay should be clean, dry and not coarse; a good grade of English china clay is satisfactory.

The water and the gelatine should be free from oil and grease. Since practically all commercial gelatines contain a small percentage of fatty acid, a small quantity of alkali, as, for example, c. c. of a 10% solution of sodium hydroxide, should be used in making up a batch of coating material.

It is necessary that the overlay shall exactly register with the printing plate for which it is made, from which it follows that the overlay in drying after the etching operation should return with great precision to its original dimensions. I have discovered that the jelly strength of the size is a factor in the shrinkage of the etching. \Vhen size that is low in jelly strength is used, the overlav when being dried after the etching operation will shrink below its original dimensions. Glue and gelatin give the best result-s.

If the coating solution is made up one day to be used the following day a preservative should be added. A small quantity of phenol may be used for this purpose.

It is desirable that there be a distinction between the color of the coating and the color of the paper base. in order that the operator may known when the paper has remained in the etching solution for the necessary length of time. F or this purpose a small quantity of some suitable coloring matter may be employed with the other ingredients, as, for example, 120 grams of 10% paranitraniline red. This color is fast to the chloride of lime etching solution. No color should be used which is water-resistant.

In order to make the coating smooth and loo uniform, it is desirable to mix and grind the ingredients in a suitable mill, as, for example, a paint mill, the hopper of which is large enough to hold an entire batch. The hopper and the receiving receptacle should be heated'to keep the material from jellifying during the grinding.

- In making up the coating, a layer of clay is placed in the bottom of the hopper of the mill; some of the water for the clay is then added, then a second layer. of clay, and so on. Before all of the clay and water are added, the coloring material is mixed into a little of the water and added to the clay. The clay may be allowed to soak for two hours or longer. i

The gelatine is thoroughly moistened with the specified quantity of water and allowed to soak for, say, two hours. The alkali and preservative are then added to the gelatine, and the gelatine dissolved by applying heat.

The clay after soaking is stirred thoroughly; the gelatine is then poured into the hopper of the mill through an SO-mesh sieve, after which the batch isagain stirred. The mill is then started.

When the grinding is completed, the application of heat to the container for the batch is discontinued and the batch permitted to jellify over night. Thefollowing morning heat is again applied to the batch so as to cause the latter to melt. After straining the batch and skimming off the bubbles, the viscosity of the batch is meas ured and water added until, after thorough stirring, the batch is of the desired viscosity. The alkali causes an'increase in the viscosity of the batch, which action increases with the time of standing. For this reason, an excess of alkali must not be used.

Any suitable apparatus may be used to apply the coating material to the paper, as, for example,the construction illustrated in mycopending application Serial No. 280,-

750, filed March 5, 1919.

In order to prevent the formation of small pits in the applied coating, it is necessary to keep the coating material free from particles of lint, greasy particles, or particles not necessarily greasy but 'not easily wet by water. The grinder, the coating machine, and all utensils must be kept free from oil,

' grease and other substances not readily miscible with water.

In handling a coating as high in sizing as the one herein described, it is difficult to prevent foaming. The difliculty may, however, be obviated or cured by avoiding violent agitation, by repeated skimming, and by using two compartments in the coating machine so that the compartments in which the paper is coated receives its supply from the bottom of the compartment into which thecoating is poured.

To prevent variations in the thickness of way, after which it is cut into sheets of convenient size, as, for example, 12x18 or 17%x22{-. The sheets are then calendered in any suitable manner, as, for example, by means of the plating method, a number of sheets being placed between zinc plates, and the whole run back and forth between two large cylinders under great pressure. In drying, the overlay paper should shrink to a point slightlybut definitely below the m1- tial size of the paper base. To obtain a coating which satisfactorily fulfils this requirement, the proportion of the gelatinoussizingto the clay body, and also the elly strength of'the sizing, should be such that the shrinkage of the whole coating composiwhen the paper is slightly stretched by the plating process. It is obvious that any slight variation in the .grain size or other properties of the clay or in the jelly strength of the sizing would necessitate a reproportioning ofjthe ingredients to secure the desired result. Thus a coated paper is obtained which will not stretch or shrink on being a second time wetted and dried, as

as adapted for use in making McKee matri-' ces, it will be understood that the various other uses.

I claim as my invention;

1. A coating composition for use in manufacturing coated paper consisting of clay, gelatine, alkali and, water (in approximately the followingproportions: clay, 39 pounds, water for the clay, 28" pounds, gelatine, 74 ounces, water for the gelatine, 15 pints, and 90 "c. c. of a 10% solution of sodium hydroxide), and a coloring material.

2. A coating composition for use in manupaper has.

factu ring coated paper consisting of clay, gelatine and Water in approximately the following proportions: clay, 39 pounds, Wa-

ter for the clay, 28 pounds, gelatine, 74

ounces, Water for the gelatine, 15 pints.

3. A coating composition for use in manufacturing coated paper comprising English china clay and grease free gelatine.

4. A coating composition for use in manufacturing coated paper comprising a mineral and gelatine free from grease and oil.

5. A bath for coating overlay paper com- .prising Water, powdered clay, a gelatinous sizing, an alkali to eliminate all traces of grease, and a preservative for the sizing.

6. A paper base coated With a composition capable of being etched and comprising powdered clay incorporated in a grease free gelatinous sizing containing a preservative.

7; An etchable coating composition for paper comprising grease free sizing material of high jelly strength, and inert body material incorporated With said sizing material, the mixture of sizing and body material being in such proportions as to produce a fac- .tor of shrinkage of the coat in drying after the coating operation, slightly but definitely greater than the expansion of the paper base When it becomes Wet during the coating operation.

In testimony whereof, I have hereunto set my hand.

HENRY N. CASE. 

